Of what importance is the regular presence of food in the gut to the normal functioning of the GI tract? As basic as this question is to nutrition and GI physiology it has not been answered. Until recently methods have not been available for maintaining animals for significant periods of time without enteral feeding. We propose to study the effect of food in the gut by examining the result of the lack of it in intravenously hyperalimented (IVH) rats and dogs. IVH rats: 1) are gastrin depleted, 2) show severe atrophy of oxyntic gland area, pancreas and intestine, 3) have drastically decreased disaccharidase levels and 4) increase their capacity for glucose transport. The last three of these can be prevented by exogenous gastrin. The objectives of the proposed research are to determine 1) the sequence and time course of the above changes plus any other involving motility and carbohydrate, fat, protein, and nucleic acid metabolism following initiation of IVH, 2) the sequence of reversal of the above changes upon resumption of oral food intake, 3) the role of specific foodstuffs in regulating activities of pancreatic and intestinal brush border enzymes, 4) the role of GI hormones in maintaining the structural and functional integrity of the gut, 5) the factors regulating endogenous gastrin levels and synthesis. These studies are of significance in the management of patients having cancer, intestinal fistulas, and others who are often treated by total parenteral feeding. The IVH method applied to rats and dogs in these studies will allow us to pose and to answer many significant physiological questions concerning the regulation of growth, gastrin levels, absorption, disaccharidase activity and motility which have never been evaluated without having to take into account the potential effects of starvation.